US9114540B2

US9114540B2 - Compliant underactuated grasper

Info

Publication number: US9114540B2
Application number: US14/552,612
Authority: US
Inventors: Mark Claffee; Nicholas Roy Corson
Original assignee: iRobot Corp
Current assignee: iRobot Corp
Priority date: 2012-11-09
Filing date: 2014-11-25
Publication date: 2015-08-25
Anticipated expiration: 2033-03-15
Also published as: US9089977B2; US20140132018A1; US20150076850A1

Abstract

A grasper includes a base, a finger, a tendon cable and a magnetic breakaway mechanism. The finger has a proximal end connected to the base by a proximal joint. The tendon cable is configured to move the finger relative to the base. The magnetic breakaway mechanism releasably couples the finger to the base.

Description

RELATED APPLICATION(S)

The present application is a continuation application of and claims priority from U.S. patent application Ser. No. 13/833,687, filed Mar. 15, 2013, which claims the benefit of and priority from U.S. Provisional Patent Application No. 61/724,517, filed Nov. 9, 2012, the disclosures of which are incorporated herein by reference in their entireties.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with support under Defense Advanced Research Projects Agency (DARPA) Contract No. W91CRB-10-C-0141 awarded by DARPA for the DARPA Autonomous Robot Manipulation-Hardware Track (ARM-H). The Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

End effectors or graspers are commonly mounted on a robotic arm and used to manipulate and/or grasp objects in a selected environment. The environment may be structured or unstructured.

SUMMARY OF THE INVENTION

According to embodiments of the present invention, a grasper includes a base, a finger, a tendon cable and a magnetic breakaway mechanism. The finger has a proximal end connected to the base by a proximal joint. The tendon cable is configured to move the finger relative to the base. The magnetic breakaway mechanism releasably couples the finger to the base.

In some embodiments, the tendon cable extends through the magnetic breakaway mechanism and to the finger. The magnetic breakaway mechanism may include: a finger submount, wherein the finger is pivotably connected to the finger submount by the proximal joint; and a base submount on the base; wherein the finger submount and the base submount are magnetically attracted to one another and the finger submount is connected to the base via the base submount. According to some embodiments, the magnetic breakaway mechanism includes at least one locator feature to re-align the finger submount with the base submount when the finger submount and the base submount are separated and re-joined. The at least one locator feature may include an annular or semi-annular groove.

In some embodiments, the magnetic breakaway mechanism is operative to release the finger to deflect relative to the base when a load exceeding a threshold load is applied to the finger.

According to embodiments of the present invention, a compliant underactuated grasper includes a base, two finger digits and a thumb digit opposing the two finger digits. The finger digits and the thumb digit each comprise: a proximal phalanx; a distal phalanx; a distal joint directly connecting the proximal phalanx to the distal phalanx, the distal joint being compliant in a first direction; a proximal joint directly connecting the proximal phalanx to the base, the proximal joint being compliant in a second direction; and a tendon cable for moving the proximal and distal phalanges, wherein the tendon cable is substantially parallel to the first direction of compliance and substantially changes the compliance of the distal joint in the first direction. The grasper further includes at least one actuator to move the finger digits and thumb digit. The thumb digit further includes a second tendon cable for selectively restraining the proximal phalanx thereof in opposition to the first tendon cable to enable movement of the distal phalanx independently of the proximal phalanx. The grasper has fewer actuators than degrees of freedom.

In some embodiments, the grasper includes a first actuator to actuate the first tendon cable of the thumb digit and a second actuator to actuate the second tendon cable of the thumb digit.

According to some embodiments, each finger digit does not include a tendon for selectively restraining the proximal phalanx thereof in opposition to the tendon cable thereof to enable movement of the distal phalanx independently of the proximal phalanx.

According to embodiments of the present invention, a compliant underactuated grasper includes a base, two finger digits and a thumb digit opposing the two finger digits. The finger digits and the thumb digit each comprise: a proximal phalanx; a distal phalanx; a distal joint directly connecting the proximal phalanx to the distal phalanx, the distal joint being compliant in a first direction; a proximal joint directly connecting the proximal phalanx to the base, the proximal joint being compliant in a second direction; and a tendon cable for moving the proximal and distal phalanges, wherein the tendon cable is substantially parallel to the first direction of compliance and substantially changes the compliance of the distal joint in the first direction. The grasper further includes at least one actuator to move the finger digits and thumb digit. The tendon cable is capable of transmitting sustained tensile loads in the range of from about 60 to 120 1 bf, exhibits low energy storage upon bending, and is robust to bend radii less than one millimeter. The grasper has fewer actuators than degrees of freedom.

In some embodiments, at least one of the finger digits and the thumb digit includes a magnetic breakaway mechanism releasably coupling the proximal joint to the base.

Further features, advantages and details of the present invention will be appreciated by those of ordinary skill in the art from a reading of the figures and the detailed description of the embodiments that follow, such description being merely illustrative of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, perspective view of a robot including a grasper according to embodiments of the invention.

FIG. 2 is a front perspective view of the grasper of FIG. 1.

FIG. 3 is a rear perspective view of the grasper of FIG. 1.

FIG. 4 is a cross-sectional view of the grasper of FIG. 1 taken along the line 4-4 of FIG. 1.

FIG. 5 is a cross-sectional view of the grasper of FIG. 1 taken along the line 5-5 of FIG. 1.

FIG. 6 is a top plan view of the grasper of FIG. 1.

FIG. 7 is a side elevational view of the grasper of FIG. 1.

FIG. 8 is a rear elevational view of the grasper of FIG. 1.

FIG. 9 is a top perspective view of a finger forming a part of the grasper of FIG. 1.

FIG. 10 is a bottom perspective view of the finger of FIG. 9.

FIG. 11 is a cross-sectional view of the finger of FIG. 9 taken along the line 11-11 of FIG. 9.

FIG. 12 is an enlarged, fragmentary, side view of the finger of FIG. 9.

FIG. 13 is a top plan view of the finger of FIG. 9.

FIG. 14 is aside view of the finger of FIG. 9.

FIG. 15 is a top perspective view of the finger of FIG. 9 and an associated magnetic breakaway system.

FIG. 16 is an exploded, fragmentary, bottom perspective view of the finger and magnetic breakaway system of FIG. 15.

FIG. 17 is an exploded, fragmentary, top perspective view of the finger and magnetic breakaway system of FIG. 15.

FIG. 18 is a cross-sectional view of the magnetic breakaway system of FIG. 15 taken along the line 18-18 of FIG. 15.

FIG. 19 is a cross-sectional view of the magnetic breakaway system of FIG. 15 taken along the line 19-19 of FIG. 15.

FIG. 20 is an exploded, fragmentary, cross-sectional, bottom perspective view of the magnetic breakaway system of FIG. 15.

FIG. 21 is a top perspective view of a base forming a part of the grasper of FIG. 1 including submounts forming a part of the magnetic breakaway system.

FIG. 22 is a fragmentary, perspective view of the finger and magnetic breakaway system of FIG. 15 illustrating operation of the magnetic breakaway system.

FIGS. 23-29 illustrate various finger configurations that can be executed by the grasper of FIG. 1.

FIGS. 30A and 30B illustrate a sequence of movements of the grasper of FIG. 1 to grab and pick up an object.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. In the drawings, the relative sizes of regions or features may be exaggerated for clarity. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

It will be understood that when an element is referred to as being “coupled” or “connected” to another element, it can be directly coupled or connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly coupled” or “directly connected” to another element, there are no intervening elements present. Like numbers refer to like elements throughout.

In addition, spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. Thus, the exemplary term “under” can encompass both an orientation of over and under. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein the expression “and/or” includes any and all combinations of one or more of the associated listed items.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Embodiments of the present invention are directed to end effectors or graspers. A grasper as disclosed herein may form part of a robot or a prosthetic apparatus. In particular, the grasper may be mounted on a robotic arm and used to manipulate and grasp objects in a structured or unstructured environment. The grasper may be employed as a grasper or “hand” of a humanoid robot and/or may comply with the criteria specified under the DARPA Autonomous Robot Manipulation Hardware (ARM-H) program.

With reference to the figures, a robot 10 (FIG. 1) according to embodiments of the invention is shown therein and includes an arm 12 and a grasper 20 rotatably coupled to the arm 12 by a wrist joint 14.

The grasper 20 includes a base assembly 30, a first finger 70, a second finger 80, and a thumb 90. The

fingers

70, 80 and the thumb 90 may be identically constructed except for their placement on the base 30 and methods and mechanisms of actuation as discussed below. Except as otherwise noted, “finger” and “fingers” also refer to the thumb 90. The grasper 20 has a primary or longitudinal axis LG-LG (FIG. 4).

The base 30 includes a first finger actuator 60, a second finger actuator 62, a thumb agonist actuator 64, a thumb antagonist actuator 66, and a finger rotation actuator 68. The

actuators

60, 62, 64, 66, 68 may be electric motors (e.g., DC motors).

Tendon cables

60A and 62A (FIG. 4) are connected to the

fingers

70 and 80, respectively, to cause controlled movement of the

fingers

70 and 80 using the

actuators

60 and 62.

Tendon cables

64A, 66A (FIG. 5) are connected to the thumb 90 to cause controlled movement of the thumb 90 using the

actuators

64 and 66, respectively. Each of the

fingers

70, 80, 90 can be pivoted at a respective proximal pin pivot joint JP about an axis FP-FP (FIG. 2) by the

tendons

60A, 62A, 64A, 66A and the

actuators

60, 62, 64, 66. Additionally, the

fingers

70 and 80 can be rotated at respective rotation joints JR about rotation axes FR-FR (FIG. 8) in opposed directions K by the actuator 68. The

fingers

70 and 80 are coupled by a linkage so that they rotate about the joints JR in tandem in opposite directions from each other. Each

finger

70, 80, 90 can also be bent about a distal compliant flexure joint JC (FIG. 1) as described below.

The base assembly 30 includes a frame 32 and a palm 34 on an operational side of the frame 32. Three magnet base submounts 160 are mounted in the frame 32 and three associated finger base submounts 40 are mounted thereon (FIG. 15). During normal operation, each submount 160 and its associated submount 40 are coupled to function effectively as a single unit. The submounts 160 of the

fingers

70 and 80 are rotatable at the joints JR.

The

fingers

70, 80, 90 may be identically or similarly constructed as discussed above. An exemplary finger 70 will be described, and it will be appreciated that this description will likewise apply to the

other fingers

80 and 90.

With reference to FIGS. 9-14, the finger 70 includes a proximal phalanx 110 and a distal phalanx 120 coupled by a compliant flexure link 130 at a compliant distal inter-phalanges flexure joint JC. The finger 70 also has a hinge feature 112 coupling the finger 70 to its finger base mount 40. The finger 70 has a longitudinal axis LF-LF. More particularly, the proximal phalanx 110 has a proximal end 110A and a distal end 110B. The distal phalanx 120 has a proximal end 120A and a distal end 120B. The hinge feature 112 is provided on the end 110A. The flexure link 130 is secured to the

ends

110B and 120A. The end 120B is free. A distal extension or plate member 140 is mounted on the end 120B.

The hinge feature 112 is pivotally coupled to a cooperating hinge feature 42 (FIG. 1) on the finger base submount 40 by a pivot pin 50, which defines the pin pivot axis FP-FP, to form the proximal pin pivot joint JP. Rotational movement of the finger 70 about the pivot joint JP is constrained to pivoting about the pivot axis FP-FP in a finger closing pivot direction F and a finger opening pivot direction H. The finger 70 defines a finger lateral plane E parallel to each of the longitudinal axis LF-LF and the pivot axis FP-FP. It will be appreciated that the orientation of the pivot axis FP-FP will vary depending on the rotational position of the submount 40 about the axis FR-FR.

In one embodiment, an angle position sensor 54 disposed in the joint JP detects the angular position of the phalanx 110 with respect to the base 30. For example, a magnetic encoder may be mounted on one part of the joint JP (e.g., the hinge feature 42) and a cooperating magnet may be mounted on another part of the joint JP (e.g., the hinge feature 112).

A biasing member 52 (FIGS. 4 and 7) is provided in the joint JP. According to some embodiments, the biasing member 52 is a torsion spring and, in particular, may be a helical torsion spring. The torsion spring 52 serves as a counter spring or bias return spring. In the absence of restraint from a tendon cable or external force, the torsion spring 52 will force the finger 70 to pivot in a direction I to a wide-open position.

The flexure link 130 is semi-rigid, flexible, resilient and compliant. In some embodiments, the flexure link 130 is formed of an elastomeric material. The flexure link 130 flexes or bends preferentially about a distal or flexure joint pivot axis FB-FB in each of an inward, primary direction M and an outward direction N. The flexure link 130 can also flex or bend in opposed sideward or lateral, secondary directions P perpendicular to or transverse to the finger closing direction F. Thus, the flexure link 130 and the joint JC have a first compliance in a first direction M and a second compliance in a second direction P. The second direction P is perpendicular or transverse to the tendon cable retraction direction H. The first compliance is greater than the second compliance (i.e., less force is required to deflect the flexure link 130 in the first direction). When relaxed and nonloaded, the flexure link 130 will elastically return to a relaxed position or state as shown in FIGS. 9-11. According to some embodiments, the proximal phalanx 110 and the distal phalanx 120 are substantially parallel or co-axial when the flexure link 130 is in its return position.

The tendon cable 60A is routed from the actuator 60, through

tendon raceways

158, 168 in the

submounts

40, 160, along the inner side of the hinge feature 112, through a tendon raceway 118 in the proximal phalanx 110, across the flexure joint JC, and through a raceway 128 in the distal phalanx 120, and is anchored to the distal phalanx 120 (e.g., in the raceway 128). The actuator 60 can draw the tendon cable 60A through the

raceways

118, 158, 168 in a direction H to pivot the finger 70 in the closing direction F. The actuator 60 can then release or pay out the tendon cable 60A in the opposite direction to permit the finger 70 to pivot in the opening direction I under the torque of the torsion spring 52.

Operation of the finger 70 (and corresponding operation of the finger 80 and the thumb 90) will now be discussed in further detail. With the finger 70 in the fully open position (FIG. 23), the actuator 60 draws the tendon cable 60A. The spring force or resistance from the torsion spring 52 is less than the stiffness or spring force or bend resistance of the flexure link 130. Therefore, assuming the proximal phalanx 110 does not encounter external resistance, as the tendon cable 60A applies tension load to the finger 70, the finger 70 will be displaced primarily about the pin pivot JP and secondarily about the flexure joint JC. That is, the proximal phalanx 110 will pivotally rotate a greater angular distance about the pivot pin axis FP-FP than the distal phalanx 120 pivotally rotates or bends about the flexure joint axis FB-FB.

If and when the proximal phalanx 110 is impeded by an external object (e.g., an object grasped) or strikes a limit (e.g., bottoms out on the base 30), a greater portion or all of the tension load of the tendon cable 60A will be applied to the flexure joint JC, and the distal phalanx 120 will then bend or rotate about the flexure joint axis FB-FB at a greater rate than the rate at which the proximal phalanx 110 rotates about the pin pivot axis FP-FP.

The differential rate of displacement of the

phalanges

110 and 120 about their respective pivot axes will depend on the relative effective spring forces of the torsion spring 52 and the flexure link 130. According to some embodiments, the spring force of the flexure joint JC is at least 8 times the spring force of the pin pivot joint JP and, in some embodiments, is in the range of from about 8 to 12 times the spring force of the pin pivot joint JP. In some embodiments the spring rate of the torsion spring 52 is great enough to fully counteract the force of gravity on the finger 70 in any intended orientation when the grasper 20 is static and not acted on by an external object. According to some embodiments, the spring force of the torsion spring 52 is between about 100 and 150 percent of the minimum force necessary to fully counteract the force of gravity on the finger 70 in any intended orientation when the grasper 20 is static and not acted on by an external object. By minimizing the torsion spring force, the designer can reduce the required spring rate of the flexure joint JC. In turn, the return forces that the actuator 60 must overcome are reduced.

Notably, the spring force of the flexure joint JC can be as high as desired and/or needed. In particular, the spring force of the flexure joint JC may be increased as the grasper is scaled up in size and used to lift larger and heavier objects.

FIGS. 1 and 23-29 show various configurations of the

fingers

70, 80, 90 that can be assumed or executed by the grasper 20.

FIG. 23 shows a wide open or ready position, wherein the

tendon cables

60A, 62A, 64A are slack, permitting the torsion springs 52 to force each

finger

70, 80, 90 to its limit in its open direction.

FIG. 1 shows the

fingers

70, 80 in a pinch configuration, which can be achieved when the

actuators

60, 62 pull the fingers 70, 80 (via the

tendon cables

60A, 62A) closed without significant resistance. For this maneuver, the finger rotation actuator 68 may first be used to rotate the

fingers

70, 80 into opposition with one another with their pivot axes FP-FP substantially parallel. FIG. 24 illustrates a modified pinch configuration being used to hold and/or manipulate an object 2 such as a flat key.

FIGS. 23, 25 and 26 show the

fingers

70, 80, 90 progressing from the wide open configuration (FIG. 23) to a power grasp configuration (FIG. 26) wherein the thumb 90 crosses the

fingers

70, 80. For this maneuver, the rotation actuator 68 may be used to rotate the

fingers

70, 80 into opposition with the thumb 90 with the pivot axes FP-FP of the

fingers

70, 80, 90 substantially parallel as shown in FIG. 25. FIG. 27 illustrates a modified power grasp configuration being used to hold and/or manipulate an object 4 such as a power tool. The exemplary power tool 4 has a handle 4A and a trigger 4B. The grasper 20 securely holds the handle 4A using the

fingers

70, 80, 90, and can also be used to operate the trigger 4B by applying and releasing tension to/from the finger 80 via the tendon cable 62A so that its distal phalanx 120 will independently bend at the flexure joint JC and press and release the trigger 4B (the proximal phalanx 110 being limited or constrained by the handle 4A).

FIG. 28 shows the

fingers

70, 80, 90 in a spherical grasp position. For this maneuver, the

fingers

70, 80 are rotated so that their pivot axes FP-FP extend at an oblique angle to the pivot axis FP-FP of the thumb 90. FIG. 29 illustrates a modified spherical grasp position wherein the grasper 20 is holding an object 6 such as a ball.

It will be appreciated that the foregoing are not exhaustive of the configurations and manipulations that can be achieved using the grasper 20.

The relationships between the lengths of the

phalanges

110 and 120 and the finger and thumb base positions can provide advantageous performance. In some embodiments, these relationships are scalable.

According to some embodiments, the length L1 (FIG. 13) of the proximal phalanx 110 of each

finger

70, 80 is greater than the length L2 of the distal phalanx 120 of the same finger. According to some embodiments, the length L1 is in the range of from about 0.60 to 0.66 times the length L2.

In some embodiments, the average distance D1 (FIG. 6) from each

finger

70, 80 base pivot joint JP to the thumb 90 pivot joint JP is in the range of from about 1.30 to 1.44 times the average proximal phalanx length L1.

According to some embodiments, the major dimension L3 (FIG. 6) of the palm 34 is in the range of from about 1.21 to 1.33 times the average proximal phalanx length L1.

In some embodiments, the spacing D2 (FIG. 6) between the pivot joints JP of the

fingers

70, 80 is in the range of from about 0.97 to 1.08 times the average proximal phalanx length L1.

The provision of fingers each having a proximal pin pivot joint and a distal flexure joint as described may provide certain advantages. The rigid pivot at the base of the finger provides pinch stability and torsional strength to facilitate fine manipulation and heavy lifting. The flexure joint at the distal joint provides robustness for abuse and enhances the ability of the finger to adapt or conform to unknown shaped objects. According to some embodiments and as shown, the pin pivot axis FP-FP of each finger is substantially parallel to the primary flexure axis FB-FB of the finger.

With reference to FIGS. 9-12, according to some embodiments, the grasper 20 is provided with a fingernail system 141. The fingernail system 141 includes a distal plate member 140 mounted on the distal phalanx 120 of each

finger

70, 80, 90 adjacent the distal end face 124A thereof. Only one of the fingers 70 will be described hereinbelow. However, it will be appreciated that this description applies likewise to the

fingers

80 and 90.

The distal plate member 140 includes a base portion 144 and a free terminal lifting edge 142A. The base portion 144 has a slot 144A and is adjustably secured to the back face 124C of the phalanx 120 by a fastener 144B such as a screw. The free edge 142A is located adjacent the end face 124A. In some cases, and as shown, the distal plate member 140 has an extension portion 142 terminating in the free edge 142A and overhanging (cantilevered) or extending axially beyond the location 147 where the plate member 140 diverges from the phalanx 120 to form a ledge. However, in other embodiments, the free edge 142A can be coincident with or inboard of the location 147.

In some embodiments, the fastener 144B and groove 144A can serve as an adjustment mechanism. More particularly, the fastener 144B can be loosened, the plate member 140 slid to position the edge 142A as desired relative to the end face 124A, and the fastener 144B then re-tightened to secure the plate member 140 in place. It will be appreciated that other suitable adjustment mechanisms can be employed.

The plate member 142 is relatively thin, at least in the region of the free edge 142A. According to some embodiments, the free edge 142A has a thickness T1 (FIG. 12) in the range of from about 0.02 inch to 0.03 inch. In some embodiments, the length L4 of the extension portion 142 from the location 147 to the free edge 142A is at least 1 mm and, in some embodiments, from about 1.5 mm to 2.5 mm. According to some embodiments, the free edge 142A is substantially parallel to the flexure joint axis FB-FB.

According to some embodiments and as shown, the end face 124A and the plate member 140 are relatively configured and arranged to define a laterally extending slot, groove or undercut 146 between the underside of the extension section 142 and the opposing surface of the end face 124A. In some embodiments and as shown, the end face 124A is shaped to cut back axially to form the undercut 146. In some embodiments, the end face 124A is rounded or curvilinear and, in some embodiments, arcuate in cross-section (i.e., in a plane perpendicular to the plane E and parallel to the longitudinal axis of the distal phalanx 120).

According to some embodiments, the depth D3 of the undercut 146 is in the range of from about 1 mm to 3 mm. According to some embodiments, the width W1 of the undercut 146 is in the range of from about 10 mm to 25 mm.

In some embodiments, the plate member 140 is rigid (e.g., formed of steel or stainless steel) and the end face 124A is relatively soft or compliant (e.g., formed of a pliable rubber). As shown, the distal phalanx 120 includes a soft pad 125 including the end face 124A. In some embodiments, the pad 125 has a durometer in the range of from about 0 Shore A to 60 Shore A and, in some embodiments, from about 10 Shore A to 40 Shore A, and the plate member 140 has a stiffness of at least about 100 GPa and, in some embodiments, at least 180 GPa.

The plate member 140 can be used to pick up, engage and/or manipulate objects in a manner not possible or that would be cumbersome without the “fingernail”. The combination of the thin, rigid plate member 140 (“fingernail”) and the pliable, soft pad 125 (“fingertip) enables the finger to capture an edge of an object therebetween (i.e., in the undercut 146). For example, if an object is disposed on a support surface (e.g., a table surface), the plate member 140 can be pressed against the support surface, then translated under the object (between the object and the support surface), and then used to lift the object. The compliant flexure joint JC compliments the functionality of the fingernail system 141. The joint compliance enables the plate member 140 to adaptively align with and maintain contact with the support surface.

With reference to FIGS. 30A and 30B, the grasper 20 is shown therein performing a sequence of steps or movements to grasp and pick up an object 2 (as shown, a relatively flat key) from a planar surface Z (e.g., a table or floor).

Initially, the key 2 is laid flat on the surface Z. With reference to FIG. 30A, the grasper 20 is positioned such that the extension section 142 of the plate member 140 of the finger 70 is placed on the surface Z proximate the side edge 2A of the key 2 with the undercut 146 and the soft pad 125 overlying the extension section 142. The phalanx 120 of the finger 80 is placed against the surface Z and driven in a direction J toward the key 2 and the finger 70, the

fingers

70 and 80 being relatively disposed in a pinching configuration. As the finger 80 is driven in the direction J, it engages the side edge 2B of the key 2 and pushes the side edge 2A onto the plate member 140 (in some embodiments, into the undercut 146 and between the extension section 142 and the soft pad 125). The phalanx 120 of the finger 80 is further driven toward the finger 70 and upward to lift the side edge 2B off the surface Z. The key 2 is thereby flipped or pivoted upwardly about its edge 2A and toward the end face 124A of the finger 70 in a direction K as shown in FIG. 30A, the edge 2A being captured between the plate member 140 and the pad 125. With reference to FIG. 30B, the finger 80 is used to continue lifting the key 2 and converged with the finger 70 until the key 2 is sandwiched between the end faces 124A of the

fingers

70 and 80, which engage the opposed faces 2D and 2C, respectively, of the key 2.

A relatively flat object such as a key (or credit card, etc.) can thus be grasped, removed from a planar surface and manipulated using the “fingernail” or fingernails” of the grasper 20 and cooperative movement of the fingers 70, 80 (and, in some embodiments, the base 30 and/or the arm 12).

In some embodiments and as shown, the axially extending front side edges 126A of the distal phalanx 120 are sharp or distinct and the front face 124B (i.e., the contact or engagement face) is substantially flat or planar (FIGS. 9 and 10). According to some embodiments, the side walls of the distal phalanx 120 forming the side edges 126A with the front face 124B are substantially planar at and adjacent the front face 124B and, in some embodiments, extend substantially perpendicular to the plane of the front face 124B. The front face 124B may be textured. As shown, these edges 126A and the front face 124B can be the edges and front face of the soft pad 125. In some embodiments, the plane of the front face 124B is substantially parallel to the pivot pin axis FP-FP and the flexure joint primary axis FB-FB.

In use, the described configuration assists in stabilizing the distal phalanges 120. For example, when the

fingers

70, 80 are used to pinch an object between the distal phalanges 120, the sharp side edges 126A and the planar front face 124B can reduce or eliminate the tendency of the distal phalanges 120 to be twisted about their flexure joints JC. The sharp edges 124A can also assist in making firm and precise engagement with an object.

In some embodiments, the distal phalanx 120 is prismatic and has a substantially rectangular cross-section. In some embodiments, the proximal phalanx 110 is also prismatic and has a substantially rectangular cross-section.

With reference to FIGS. 15-22, the grasper 20 may also be provided with a magnetic breakaway system or mechanism 150 coupling each of the

fingers

70, 80, 90 to the base 30. The breakaway features for each of the

fingers

70, 80, 90 may be substantially the same or similar and therefore the description below with regard to the finger 70 likewise applies to the

fingers

80 and 90.

The magnetic breakaway system 150 includes the finger base submount 40 and the magnet base submount 160. A magnet 166 is fixed in the submount 160 and a ferromagnetic member or plate 156 (e.g., formed of steel) is affixed in the submount 40. A magnetic field concentrator 153 may be provided in the submount 160.

The submount 40 has a circumferentially extending locator flange 152 defining a rotational alignment slot 154 therein. The submount 160 has a circumferentially extending, semi-annular locator groove 162 having a rotational alignment tab 164 therein. The locator flange 152 is seated in the locator groove 162 such that the tab 164 is seated in the slot 154. The tendon cable 60A extends through

axial tendon raceways

158 and 168 defined in the

submounts

40 and 160, respectively. Likewise, in the case of the finger 80, the tendon cable 62A extends through the

raceways

158 and 168. In the case of the thumb 90, the

tendon cables

64A and 66A extend through respective ones of the

axially extending raceways

158 and 168.

In use, the magnetic breakaway system 150 can serve to decouple the

fingers

70, 80, 90 from the base 30 to prevent or reduce the risk of damage to the finger or joint. When a load on a finger exceeds a prescribed threshold load, the magnetic attraction between the

components

156 and 166 is overcome and the submount 40 separates (partially or fully) from the submount 160. For example, the finger 70 and its submount 40 may be deflected away from the cooperating submount 160 in a deflection direction G as shown in FIG. 22. When the load on the finger is relieved (e.g., by removing an object or operating the associated actuator to pay out the tendon cable), the magnetic attraction or tension in the tendon cable will again draw the

submounts

40 and 160 together. For example, the finger 70 and its submount 40 may return or pivot back onto the cooperating submount 160 in a return direction H as shown in FIG. 22. The pull force of the tendon through the

raceways

158, 168 will tend to draw the

submounts

40, 160 into coaxial alignment. In the case of a small breakaway deflection of the submount 40 from the submount 160, the shapes of the locator features 152, 154, 162, 164 may automatically guide the

submounts

40 and 160 back into rotational alignment, whereupon the

submounts

40 and 160 will again interlock. Applying additional tension to the tendon cable may also rotate the

submounts

40 and 160 into rotational alignment. In some cases, the

submounts

40 and 160 can be rotationally aligned by rotating the submount 160 using the actuator 68. The submount 160 will slidably rotate relative to the corresponding submount 40 until their locator features align, whereupon the

submounts

40 and 160 will nest and interlock. In some cases, it may be necessary to manually realign and reseat the

submounts

40 and 160.

In some embodiments, the magnetic breakaway system 150 does not compromise the capability of the grasper 20 to lift heavy objects. Because the tendon cable or cables run axially through both of the

submounts

40, 160 and substantially perpendicular to the face of the magnet 166, the tendon cables pull the

submounts

40, 160 together. Typically, the

submounts

40 and 160 will only be dislodged by twisting force on the fingers.

As mentioned above and as shown in FIG. 5, the thumb 90 is provided with two

independent tendon cables

64A and 66A connected to corresponding

actuators

64 and 66. The tendon cable 64A may be regarded as an agonist tendon and the tendon cable 66A may be regarded as an antagonist tendon.

The tendon cable 64A is routed to and anchored to the distal phalanx 120 of the thumb 90 in the same manner as described above. The tendon cable 66A is routed through the

outer raceways

158, 168, over the hinge feature 42, and anchored to the back side of the proximal phalanx 110 by a screw 43.

In addition to being operable in the same manner as described above for the

fingers

70, 80 using the tendon cable 64A, the

tendon cables

64A and 66A can be used together to control movement of the distal phalanx 120 of the thumb 90 independently of its proximal phalanx 110. More particularly, the tendon cable 66A can be used to hold the proximal phalanx 110 in place, effectively stalling the proximal phalanx 110 against further rotation in the closing direction F, while the actuator 64 draws on the tendon cable 64A. Because the proximal phalanx 110 is held in place, the distal phalanx 120 is independently bent at the flexure joint JC in the direction M without simultaneous pivoting of the proximal phalanx 110 in the closing direction F. The tendon cable 66A can be extended to permit the distal phalanx 120 to elastically bend back in the direction N about the flexure joint JC.

According to some embodiments, the

tendon cables

60A, 62A, 64A, 66A are capable of transmitting sustained tensile loads in the range of from about 60 to 120 1 bf, exhibit low energy storage upon bending, and are robust to bend radii less than one millimeter.

The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the invention.

Claims

That which is claimed is:

1. A grasper comprising:

a base;

a first finger having a proximal end connected to the base by a first proximal joint;

a first tendon cable configured to move the first finger relative to the base;

a second finger having a proximal end connected to the base by a second proximal joint;

a second tendon cable configured to move the second finger relative to the base; and

a magnetic breakaway mechanism releasably coupling the first finger to the base to permit the first finger to decouple from the base and thereafter recouple with the base independently of the second finger;

wherein the first tendon cable extends through the magnetic breakaway mechanism and to the first finger.

2. The grasper of claim 1 further including a second magnetic breakaway mechanism releasably coupling the second finger to the base to permit the second finger to decouple from the base independently of the first finger.

3. The grasper of claim 2 wherein:

the first tendon cable extends through the first magnetic breakaway mechanism and to the first finger; and

the second tendon cable extends through the second magnetic breakaway mechanism and to the second finger.

4. The grasper of claim 1 wherein the magnetic breakaway mechanism includes:

a finger submount, wherein the finger is pivotably connected to the finger submount by the proximal joint; and

a base submount on the base;

wherein the finger submount and the base submount are magnetically attracted to one another and the finger submount is connected to the base via the base submount.

5. The grasper of claim 4 wherein the magnetic breakaway mechanism includes at least one locator feature to re-align the finger submount with the base submount when the finger submount and the base submount are separated and re-joined.

6. The grasper of claim 5 wherein:

the magnetic breakaway mechanism includes a finger locator feature on the finger submount and a base locator feature on the base submount; and

the finger locator feature and the base locator feature cooperate to guide the finger submount and the base submount back into a prescribed rotational alignment when the first finger is separated from and rejoined with the base.

7. The grasper of claim 4 wherein:

the finger is decoupled from the base by separating the finger submount from the base submount; and

the magnetic breakaway mechanism is configured to rejoin the finger submount with the base submount responsive to a pull force on the first tendon cable.

8. The grasper of claim 4 wherein the first tendon cable extends through each of the finger submount and the base submount.

9. The grasper of claim 1 wherein the magnetic breakaway mechanism is operative to release the first finger to deflect relative to the base when a load exceeding a threshold load is applied to the first finger.

10. The grasper of claim 1 wherein each of the first and second tendon cables is capable of transmitting sustained tensile loads in the range of from about 60 to 120 1 bf, exhibits low energy storage upon bending, and is robust to bend radii less than one millimeter.

11. The grasper of claim 1 wherein the grasper is configured such that, after the first finger is decoupled from the base, the first finger can be recoupled to the base by magnetic attraction of the magnetic breakaway mechanism or a tension in the first tendon cable.

12. The grasper of claim 1 wherein the magnetic breakaway mechanism is configured to recouple the first finger with the base responsive to a pull force on the first tendon cable.

13. A compliant underactuated grasper comprising:

a base;

two finger digits and a thumb digit opposing the two finger digits, wherein the finger digits and the thumb digit each comprise:

a proximal phalanx;

a distal phalanx;

a distal joint directly connecting the proximal phalanx to the distal phalanx, the distal joint being compliant in a first direction;

a proximal joint directly connecting the proximal phalanx to the base, the proximal joint being compliant in a second direction; and

a tendon cable for moving the proximal and distal phalanges, wherein the tendon cable is substantially parallel to the first direction of compliance and substantially changes the compliance of the distal joint in the first direction; and

at least one actuator to move the finger digits and thumb digit;

wherein the thumb digit further includes a second tendon cable for selectively restraining the proximal phalanx thereof in opposition to the first tendon cable to enable movement of the distal phalanx independently of the proximal phalanx; and

wherein the grasper has fewer actuators than degrees of freedom.

14. The grasper of claim 13 including a first actuator to actuate the first tendon cable of the thumb digit and a second actuator to actuate the second tendon cable of the thumb digit.

15. The grasper of claim 13 wherein each finger digit does not include a tendon for selectively restraining the proximal phalanx thereof in opposition to the tendon cable thereof to enable movement of the distal phalanx independently of the proximal phalanx.

16. The grasper of claim 13 wherein each of the tendon cables is capable of transmitting sustained tensile loads in the range of from about 60 to 120 1 bf, exhibits low energy storage upon bending, and is robust to bend radii less than one millimeter.